The present invention relates generally to radio frequency architecture, and more particularly, to passive interference cancellation.
In general, extraneous energy, from natural or man-made sources, that impedes the reception of desired signals is termed as interference. Interference may involve a radio emission from another transmitter at approximately the same frequency, or having a harmonic or spurious frequency approximately the same as, another emission of interest to a given recipient. In both situations, the reception of the desired signal by the intended recipient may be impeded.
Several interference cancellation techniques currently exist to reduce the effects of interference. One such technique is an interference filter. An interference filter reflects or absorbs one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. An interference filter may be high-pass, low-pass, or bandpass. Interference filters are wavelength-selective. However, an interference filter may only be used if the interference signal and the desired signal are at different frequencies. Accordingly, an interference filter would not be feasible in a situation where two radios are operating at the same frequency band.
Another technique that may be used in reducing interference is blanking the input to the receiver during the time the interference is present. However, blanking involves blocking all signals so that the receiver may not receive any signals. Accordingly, this technique is overreaching.
Yet another technique that may be used in reducing interference is a band-reject filter. A band-reject filter attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. A band-reject filter may be designed to stop the interference but will also reject the desired signal if it is in the same frequency band. Accordingly, this technique would not be feasible when two radios are operating at the same frequency band.